A diesel particulate filter (DPF) may be used to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. A soot sensor may be located downstream from the DPF and may be configured to determine whether or not a soot concentration in the exhaust gas is within acceptable levels.
The inventors herein have recognized examples wherein the soot sensor reading may not represent the actual average soot concentration. For example many DPF cracks may originate close to the DPF circumference area of the exhaust conduit. Accordingly, the concentration of soot closer to the conduit center may be lower than average levels, and higher than average levels at near the conduit circumference. In addition, many applications require that the on board diagnostic soot sensor be located a short distance downstream from the DPF exit cone where soot distribution is usually very poor due to a lack of distance for adequate soot particulates redistribution. The soot sensor may extend into, for example, a three to four inch exhaust pipe diameter only about one inch.
Efforts have been made to provide better exhaust stream soot concentration readings. For example, U.S. Pat. No. 8,225,648 provides a particulate matter sensor for sensing particulate matter present in exhaust gases in a conduit which attempts to solve the problem of undesirable spikes in the output signal of the particulate matter sensor which may be caused when large particles impinge upon the electrodes of the sensor. The disclosed device provides an inner shield surrounding a sensing face and an inner shield inlet passage for admitting exhaust gases to be sensed. The inner shield also has an exit passage to allow exhaust gases to exit. An outer shield surrounds a portion of the inner shield to define an outer shield chamber that extends axially beyond the inner shield and includes an outer shield inlet passage for communicating exhaust gases into the outer shield chamber from the upstream end of the exhaust conduit. Exhaust gases enter the inner shield from the outer shield inlet chamber.
The inventors of the present application have recognized a number of problems with the above approach. For example, the disclosed attempt appears to simply change the location within the exhaust conduit from which the exhaust gas is sampled. The disclosed attempt does not, however, provide a sample of exhaust which better represents the overall concentration of soot in the exhaust stream.
The inventors herein provide a system including a perforated barrier disposed within an exhaust stream downstream from the engine cylinder(s). The perforated barrier may divide the exhaust stream radially and longitudinally. The system may also include a mixing surface coupled with the perforated barrier. The mixing surface may define a path within the exhaust stream to impart a swirl to the exhaust stream. In this way, any soot that may be in the exhaust stream may be better mixed into the exhaust stream to provide a more homogeneous mixture. In this way, the soot sensor may provide a more accurate reading of the amount of soot that may be present in the exhaust stream. Using both flow impingement and swirling together may tend to improve flow mixing, and may provide improved performance with less pressure loss.
The perforated barrier may have a circumferential edge in substantial sealing engagement with an inner diameter wall of an exhaust conduit. The barrier may define a surface which extends upstream from the circumferential edge while extending in a radial direction from the inner diameter wall. In this way, as exhaust gas flows across the barrier it may enter a region between the circumferential edge of the exhaust conduit and the barrier outer surface. The barrier may divide the exhaust conduit into two parts, and consequently two exhaust flow paths, an upstream path and a downstream path. Flow in upstream path may pass through the perforated holes on the perforated barrier to exit to the downstream path. Since the perforated holes may be located at circumference of the barrier surface, the flow direction may be significantly pointed toward the center line of exhaust conduit. The mixing surface coupled with the perforated barrier may create a swirling flow. As flow enters the region between exhaust conduit and cone outer surface area, it may follow the curve of the mixing surface and flow rotation may be generated before it passes through the perforated holes. As the flow exits from perforated holes, the swirling momentum may carry on inside the perforated barrier and help flow mixing. With those two flow mechanisms, soot particulates may be more uniformly distributed downstream of the perforated barrier forming an effective soot mixer. In this way, the soot sensor can detect soot leakage within short distance from the DPF.
Embodiments may provide a system including a conduit for passing a stream of exhaust from a combustion chamber of an internal combustion engine. An exhaust gas sensor may be located within the conduit. A wall may be located within the conduit upstream from the exhaust gas sensor. The shape of the wall may at least approximate a cone and may have an upstream portion with a first outer diameter and a downstream portion with a second outer diameter. The second outer diameter may be larger than the first outer diameter. A plurality of passages may be in the wall. One or more edges may be coupled with the wall and may extending axially and radially within the conduit. In this way the edges may impart at least a partial swirl to the flow of exhaust, and the configuration of the wall and the plurality of passages may tend to intermix relatively upstream exhaust with relatively downstream exhaust. In this way the exhaust may be more thoroughly mixed even a relatively short distance from the DPF.
Various embodiments may provide a system including a circular exhaust pipe having a perforated bell housing with an open end of the bell facing downstream. A plurality of fins may extend helically around an outer surface of the perforated bell. In this way, soot that may be present in the exhaust stream may be more homogenously mixed into the exhaust stream which may provide a more accurate exhaust sample to be sensed by the soot sensor.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.